The present invention relates generally to data processing systems and, more particularly, to a mechanism for providing a multiple level undo/redo capability in operating systems and application programs.
A single-level undo mechanism is provided by software packages, such as the Microsoft Word, version 5.0, word processing package, which is sold by Microsoft Corporation of Redmond, Washington. The single level undo mechanism allows a user command to be undone (i.e., the effects of the sand are reversed) after the command has already been performed. The undo command is typically performed by selecting a menu item that lists the undo command as an option. The user is limited to a single level of undoing of commands and, thus, can only reverse the most recently executed command.
In accordance with a first aspect of the present invention, a method is practiced in a data processing system having memory means and at least one processor that is responsive to user commands. In this method, a log of user commands that were executed by the processor is stored in the memory means. A first user command stored in a log is undone so as to reverse the effect of the first user command. Subsequently, a next user command stored in the log is undone so as to reverse the effect of the next sequential user command.
In accordance with another aspect of the present invention, a log of at least two user commands is stored in the memory means. User commands stored in the log are undone so as to reverse the effects of at least two user commands. At least two of the undone user commands are then redone so as to again execute those commands.
In accordance with a further aspect of the present invention, a list of a plurality of user commands is stored in the memory means in a sequence ranging from a selected user command that has been executed by a processor to a most recently executed user command. The effects of all of the user commands stored in a sequence of the list are undone so as to return the processor to reverse the effects of the user commands in the sequence.
In accordance with still another aspect of the present invention, a list of a plurality of user commands is stored in the memory means. The list includes user commands that have been undone. The user commands that have been undone are again executed by the processor.